Laminated Busbar Insulation Materials: Flexible And Rigid Characteristics And Key Parameter Analysis

 

Against the background of increasing demand for high-voltage electrical systems and power density integration, the selection of insulation materials for laminated busbars has become a core factor in determining their reliability and performance. Starting from material properties, application scenarios, and key technical parameters, this article systematically analyzes the technical differences between flexible insulation and rigid insulation and provides professional references for engineers to select materials under different working conditions.

 

 

 

The insulation system of Laminated Copper BusBar is composed of flexible insulation and rigid insulation, which achieve a balance between electrical insulation, mechanical protection, and environmental adaptation through collaborative design.

 

1. Flexible insulation materials: core protection between conductor layers
Flexible insulation materials are laminated on the surface of conductors in the form of thin films. The core function is to achieve insulation sealing between conductors and adapt to the bending and forming of complex structures.

(1) Polyester film (PET)
Performance advantages:
Temperature adaptability: Long-term working temperature of 105°C (RTI certification), meeting the service life of more than 20 years in most industrial scenarios
Mechanical ductility: Elongation at break >100%, no tearing risk when bending radius ≤5mm, suitable for the complex structure hemming process
Electrical characteristics:
Flame retardant grade UL 94V-0 (thickness ≥50μm)
Relative tracking index (CTI) ≥600, supporting creepage distance optimization design (1kV corresponding creepage distance can be reduced to 8mm)
Process adaptation: Transparent/white standard thickness optional (50/125/250/350μm), compatible with automated lamination production line

Typical applications: 800V high-voltage platform for new energy vehicles, industrial servo drives (working voltage ≤1500V)

 

(2) Polyimide film (PI)
Performance advantages:
High temperature tolerance: RTI>200°C, suitable for welding process (short-term temperature resistance 300°C) and harsh aerospace environment
Flame retardant properties: Intrinsic UL 94V-0 rating, no additional flame retardant additives required
Structural characteristics: 30% harder than PET, edge sealing accuracy ±0.05mm, suitable for mechanical stress stability under a high-voltage environment

Application limitations: CTI≤200, only suitable for low-voltage scenarios below 600V
The cost is 3-5 times that of PET, the thickness range is 25-50μm, and the ductility is 70% (lower than PET)

 

2. Rigid insulation material: system-level insulation support
Rigid insulation is filled between Laminated Inverter Busbars components in the form of sheets and the high voltage insulation requirements are met through thickness design:

Material selection: Glass fiber-reinforced polyester (such as FR-4 derivative materials)
Core parameters: Breakdown voltage ≥15kV/mm (1mm thickness corresponds to 1500V working voltage). Partial discharge inception voltage (PDIV)>1.5 times rated voltage (1000V system PDIV≥1500V)
Design criteria: Follow the "1mm/kV" thickness principle (e.g. 4800V DC system uses 5mm thickness, leaving a 20% ​​safety margin)

 

 

 

 

1. Temperature reliability parameters

 

Parameter	Definition	PET characteristics	PI characteristics	Application impact
RTI	Relative temperature index (UL746 standard)	105°C (20,000 hours life)	>200°C (10,000 hours life)	PI is preferred in high-temperature environment
Arrhenius coefficient	Temperature-life relationship index	Life is halved for every 10°C temperature rise	Same rule	The design needs to be combined with the working temperature curve

 

2. Electrical safety parameters
CTI (Comparative Tracking Index): PET's CTI ≥ 600, suitable for a pollution level 3 (IEC 60587) environment, and creepage distance can be designed according to the material group. PI's CTI ≤ 200, is only suitable for pollution level 1 environment, creepage distance needs to be increased by 100%

Breakdown field strength: The breakdown field strength of the flexible insulating film is ≥ 25kV/mm (50μm thickness corresponds to 1.25kV safe working voltage), and the breakdown field strength of the rigid insulating sheet is ≥ 15kV/mm (depending on glass fiber content).

 

3. Mechanical performance parameters
Elongation: PET ≥ 100% vs PI ≈ 70%, determines the ability to form complex curved surfaces (e.g., the elongation at the sharp bend of the conductor must be > 80%)
Peel strength: The interface peel strength after lamination is ≥ 5N/mm (ASTM D3330 standard), ensuring no delamination under hot and cold cycles (-40°C ~ 125°C)

 

 

Application dimensions	Industrial high voltage system (1000-6000V DC)	Automotive electric drive system (400-800V DC)	Key points for technical decisions
Insulation system	Flexible PET + rigid glass fiber polyester	Single-layer flexible PI/PET	Voltage level determines whether rigid support is required
Core parameters	CTI>600, PDIV>1.5Ue	RTI≥125°C, vibration resistance 20g	Polluted environment vs. space compactness
Life requirements	25 years @85°C	5 years @125°C	Arrhenius model accurate calculation
Process focus	Creepage distance optimization (minimized volume)	Welding compatibility (component integration requirements)	Surface treatment vs. high-temperature resistant coating

 

 

1. Nano-composite film:
PET film modified with silica nanoparticles increases CTI to 800+ and breakdown field strength by 20%, which is suitable for high salt spray environments such as offshore wind power.

2. Flexible fire retardant coating:
Water-based epoxy resin-based coating technology achieves UL 94V-0 flame retardancy at a thickness of 50μm, replaces the traditional lamination process, and reduces weight by 30%.

3. Intelligent insulation monitoring:
Embed a conductive fiber network in the rigid insulation layer, monitor insulation aging in real-time through resistance changes (accuracy ±5%), and warned of partial discharge risks.

 

 

The selection of insulation materials for laminated busbars is a multi-objective optimization process of electrical performance, mechanical reliability, and cost. The ductility of flexible insulation and the withstand voltage of rigid insulation need to be combined and designed according to specific working conditions (voltage level, temperature profile, environmental conditions). As wide bandgap devices drive the system to evolve towards high frequency and high voltage, new insulation materials with high CTI, high-temperature resistance, and integrated monitoring functions will become the focus of industry innovation.